Friday, December 30, 2011

May the Force Be With You

I once commented that I'm the cycling equivalent of a Mustang II. Well, after spending the last few months in the gym, I can now say with great confidence that I am the cycling equivalent of a Mustang II King Cobra.

What I'm saying is that force is no longer my limiter. I achieved my goal of doing "step ups" with 90% of my body weight on my shoulders. Six sets of six reps per leg.

It's safe to say I can make some torque (twisting force) at this point. It remains to be seen if I can convert the gains from the gym to gains on the bike. I know I need to do some leg speed work to make that happen. It's been a long time since I've gone out and just spun the hell out of the pedals. (While my cruising cadence is in the upper 80s, I have terrible form above 120rpm, a far cry from the days when I could spin out my 42x23 at 22mph.)

Why should I worry about leg speed? (About to get all mathematical up in here.)

Power = torque at speed. Most folks are familiar with the term "horsepower" when talking about cars. It's a number used to describe an engine's ability to make torque at high RPMs.

A couple of somewhat correct assumptions, correct enough for an example: A 70s Mustang II King Cobra and an 80s Honda CRX make about the same horsepower. The Mustang II's post-EPA/pre-EFI V8 makes about 200lb-ft of torque at roughly 2,000 rpm. A Honda CRX's modern multivalve four cylinder is making 120lb-ft of torque at 5,000 rpm.

Yes, the Mustang makes more torque, but at a lower RPM. The game changes when gearing is introduced.

Assuming a tire circumference of 80 inches for both cars, we arrive at 792 rpm at the tire at 60 miles per hour.

If both cars are geared to deliver peak torque at 60 miles per hour (they aren't in real life, but we can pretend they are for the sake of this example), the Mustang's final drive ratio is 2.53 and the Honda's is 6.31. This means the Mustang's engine and transmission combination is putting down 506 lb-ft to the wheels at 60mph while the Honda is putting down 757.

Having 50% more twisting force at your disposal is a clear advantage when accelerating, regardless of weight differences. Not just for sprinting, but also for climbing and battling the wind.

This is why I need to do speed work.

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